The recordheader is followed by the data contents of the columns. Columns that are NULL are omitted.
记录头的后面是字段的内容，其中空字段被忽略。
2
For each non-NULL variable-length field, the recordheader contains the length of the column in one or two bytes.
对于每个非空的变长字段，记录头使用一或两个字节包含了列的长度。
3
We take the result and add a recordheader byte "0x14" to indicate "finished" and length bytes "00 00 0c" to indicate that we're sending 12 bytes of verify data.